Trellis-coded multiple-pulse-position modulation for wireless infrared communications

We present new trellis codes based on multiple-pulse-position modulation (MPPM) for wireless infrared communication. We assume that the receiver uses maximum-likelihood sequence detection to mitigate the effects of channel dispersion, which we model using a first-order lowpass filter. Compared to trellis codes based on PPM, the new codes are less sensitive to multipath dispersion and offer better power efficiency when the desired bit rate is large, compared with the channel bandwidth. For example, when the bit rate equals the bandwidth, trellis-coded (17 2)-MPPM requires 1.4 dB less optical power than trellis-coded 16-PPM having the same constraint length.     

Performance of Alamouti transmit diversity over time-varying Rayleigh-fading channels

We analyze the impact of a time-varying Rayleigh-fading channel on the performance of an Alamouti transmit-diversity scheme. We propose several optimal and suboptimal detection strategies for mitigating the effects of a time-varying channel, and derive expressions for their bit-error probability as a function of the channel correlation coefficient /spl rho/. We find that the maximum-likelihood detector that optimally compensates for the time-varying channel is very tolerant to time-varying fading, attaining full diversity order even for the extreme case of /spl rho/=0. In contrast, although lower in complexity, the suboptimal schemes suffer a diversity penalty and are thus suitable only for slowly fading channels.     

Supervised learning and frequency domain averaging-based adaptive channel estimation scheme for filterbank multicarrier with offset quadrature amplitude modulation

Filterbank multicarrier with offset quadrature amplitude modulation (FBMC-OQAM) is an attractive alternative to the orthogonal frequency division multiplexing (OFDM) modulation technique. In comparison with OFDM, the FBMC-OQAM signal has better spectral confinement and higher spectral efficiency and tolerance to synchronization errors, primarily due to per-subcarrier filtering using a frequency-time localized prototype filter. However, the filtering process introduces intrinsic interference among the symbols and complicates channel estimation (CE). An efficient way to improve the CE in FBMC-OQAM is using a technique known as windowed frequency domain averaging (FDA); however, it requires a priori knowledge of the window length parameter which is set based on the channel's frequency selectivity (FS). As the channel's FS is not fixed and not a priori known, we propose a k-nearest neighbor-based machine learning algorithm to classify the FS and decide on the FDA's window length. A comparative theoretical analysis of the mean-squared error (MSE) is performed to prove the proposed CE scheme's effectiveness, validated through extensive simulations. The adaptive CE scheme is shown to yield a reduction in CE-MSE and improved bit error rates compared with the popular preamble-based CE schemes for FBMC-OQAM, without a priori knowledge of channel's frequency selectivity.     

VIP10高速运算放大器的PSPICE数据库

从零开始创建运算放大器的SPICE电路仿真模型不仅困难而且很费时间。美国国家半导体公司建立了OrCAD Capture数据库(nationalhighspeed.olb)以及PSPICE电路模型数据库(nationalhighspeed.lib),用以存储业内领先的 VIP10工艺的高速运算放大器资料,其中包括 LMH 系列高速运算放大器的性能模型及运算放大器的电路原理图符号。登录amplifiers.national.com网页便可下载这两个数据库的资料。VIP10 工艺技术是一种高速的电介质绝缘的互补双极集成电路技术,可以将深沟技术应用到压焊晶片上实现完全的电介质绝缘,以及最佳的高速放大器性能…     

Adhesion studies for probiotics: need for validation and refinement

Adhesion of probiotic bacteria to intestinal epithelial cells is regarded as a prerequisite to exert beneficial health effects. Human intestinal epithelial lines, like Caco-2 or HT-29 cells, have been extensively used to select for adhesive strains in vitro. Adhesion to intestinal mucus has been used to a lesser extent. However, to date, there has been no standardization of the conditions used in in vitro adhesion assays. As a consequence, results obtained in different laboratories using identical strains, but different assay conditions, show great variability. This lack of standardization complicates the interpretation of data and discrepancies emerge on what is meant by effective adhesion. A critical validation of in vitro adhesion is essential for the food industry, using adhesion assays as predicitve screening tools to assess new probiotic strains. In this review we summarize a comparative study on adhesion of the well characterized probiotic bacteria L. johnsonii La1 and L. rhamnosus GG with respect to the influence of bacterial growth conditions, growth phase, buffer, pH, and mucus on adhesion properties. The results are employed in the current scientific discussion to allow a critical evaluation on the reliability of the in vitro assays.     

Passive coupling of InGaAsP/InP laser array and singlemode fibres using silicon waferboard

Passive alignment of semiconductor lasers and singlemode fibres has been achieved for the first time using a micro-machined silicon substrate. Mechanical alignment features fabricated on the substrate surface were used to align the active regions of an InGaAsP/InP laser array to four singlemode fibres held in V grooves. Optical coupling efficiencies have been achieved that are comparable to values obtained using the conventional technique of active fibre manipulation. The approach, called silicon waferboard, offers the potential for low-cost optoelectronic device packaging as well as a means for dense hybrid integration of optoelectronic, electronic and optical components required for multifibre, multichip systems.<>     

Energy cost and error performance of range-aware, anchor-free localization algorithms

Many applications that use sensor data from a wireless sensor network (WSN) require corresponding node position information as well. Therefore, it is not surprising that a common figure of merit for localization algorithms is the accuracy of the position estimate produced. Similarly, the amount of communication required by a localization algorithm is often of paramount interest as well since it is common knowledge that communication expends the most energy in a WSN. However, localization algorithms seldom characterize their communication cost. Furthermore, when they do it is often merely qualitative and is typically described as “expensive”. For two types of range-aware, anchor-free localization algorithms we found the opposite to be true. Rather than being expensive, the communication costs were quite modest. So much so that we maintain range-aware, anchor-free localization algorithms should be chosen on the basis of the accuracy required by the intended application independent of the communication cost.In this paper, we examine the effect of node degree, node distribution, range error and network size on distance error and communication cost for both incremental and concurrent versions of range-aware, anchor-free algorithms. The concurrent algorithm is twice as accurate as the incremental, but less efficient. Furthermore, node degree influences the energy cost of the algorithms the most, but neither algorithm uses more than a surprisingly small 0.8% of a 560 mA h battery. This result indicates less energy efficient localization algorithms can be tolerated, especially if they provide better accuracy. Furthermore, if energy does need to be conserved, there is not much savings available within the localization algorithm and savings must be found in other areas such as the MAC protocol or routing algorithm.     

Effects of Ar and O2 additives on photopatternable sol-gel etching in an SF6-based plasma for planar lightwave circuit fabrication

We present a novel study of the interaction of SF₆-based plasmas with sol-gel materials in a parallel plate reactive ion etching (RIE) system. The purpose of these experiments was to obtain quantitative measures and optimisation of the RIE parameters, which can be used in the microfabrication of planar lightwave circuit (PLC) devices. The sulfur hexafluoride chemistry is chosen due to its excellent etching properties of SiO₂, which is one of the components of the photopatternable sol-gel materials and is not present in typical photoresist materials. Fast process etching rate and good selectivity is achieved by varying SF₆ flow and power delivered to the electrodes. The study also reveals a marginal influence of oxygen and argon flow on the character of the sol-gel etching. The experimental data obtained can be used as a reference for any sol-gel devices fabricated using widely available RIE reactors.     

用于电源、继电器和螺线管的协同式线路保护

在各种新型先进设备上实施协同式电路保护可有助于提高设备可靠性、减少元器件数量,并使其符合严格的安规要求。协同式方法能够帮助保护电源、继电器和螺线管,避免因线路故障或过载造成电流增大以及尖峰电压或暴露在稳态过压状态带来的危害。     

Iterative timing recovery

The last decade has seen the development of iteratively decodable error-control codes of unprecedented power, whose large coding gains enable reliable communication at very low signal-to-noise ratio (SNR). A by-product of this trend is that timing recovery must be performed at an SNR lower than ever before. Conventional timing recovery ignores the presence or error-control coding and thus doomed to fail when the SNR is low enough. This article describes the iterative timing recovery, a method for implementing timing recovery in cooperation with iterative error-control decoding so as to approximate a more complicated receiver that jointly solves the timing recovery and decoding problems.